| The function of the neutron absorbing material in the nuclear reactor is to absorb the neutrons,thus realizing the start-up,shutdown and power regulation of the reactor.The elements with high neutron absorption cross sections are:B,Hf,Ag,In,Cd,Eu,Gd,Dy,etc.B4C has the advantages of high thermal neutron absorption cross section,strong corrosion resistance,low density,and the disadvantages of easily oxidized and irradiation swelling;Ag-In-Cd material has the advantages of high thermal neutron absorption cross section,good corrosion resistance,good processing performance,and the disadvantages of irradiation swelling and readily declining of its nuclear performance with time;Hf alloy has the advantages of large absorption cross-section,good corrosion resistance and good processability,and the disadvantages of high density,high cost.Eu has become a research hotspot because of its large neutron absorption cross section,long service period and low radiation swelling rate.The high chemical activity and poor corrosion resistance of metal Eu are improved by using its oxide compounds Eu2HfxOx or Eu2ZrxOy.To prepare the Eu2O3-HfO2/ZrO2 ceramic absorbing material,the co-precipitation process,the influences of composition on the crystal structure and micromorphology of precursor and composite oxide powders,and the sintering properties of the composite ceramics were studied,and the main achievments of the study are as follow:(1)with Eu2O3:HfO2/ZrO2=1:1,1:2,1:7 ceramic neutron absorbing materials as the research object,the technological route of preparing Eu2O3:HfO2/ZrO2 ceramic neutron absorbing materials was explored and established:wet co-precipitation-high temperature calcination-high energy ball milling-cold isostatic pressing-high temperature sintering,the preparation parameters of crack-free ceramic absorbers Eu2O3-HfO2 and Eu2O3-ZrO2 were optimized.(2)the effect of Eu content on the morphology of Eu2O3-HfO2 powder was studied by using oxide powder Eu2O3:HfO2=1:1,1:2,1:7 as the research object.The results show that Eu2O3:HfO2=1:1 is Eu2O3 and Eu2HfxOy rich Eu phase,Eu2O3:HfO2=1:2 is Eu2Hf2O7,Eu2O3:HWO2=1:7 is HfO2 and Eu2HfxOy rich phase,the morphology of europium oxide is regular crystal with large size,Eu2HfxOy rich Eu phase is irregular agglomerate,and Eu2HfxOy rich HF phase is regular crystalline agglomerate.In addition,the growth of precursor and sintered crystal is inherited to some extent.When the ratio of europium oxide to Eu2Hf2O7 was in accordance with the excess of Eu2Hf2O7 and stoichiometry,the preferential nucleation and growth trend of europium oxide were observed.(3)in this paper,the thermal conductivity,corrosion resistance and high temperature phase stability of Eu2O3:HfO2/ZrO2=1:7 ceramics were studied.The results show that the two ceramics have no phase transition at 25℃,400℃,800℃ and 1200℃,and the thermal conductivity of Eu2O3:HfO2=1:7 and Eu2O3:ZrO2=1:7 at 25℃ are 1.455 W/(m·K)and 1.525 W/(m·K)respectively The thermal conductivity at 350℃ is 1.381 W-m/K and 1.344 W/(m·K),the oxidation weight gain of Eu2O3:ZrO2=1:7 and Eu2O3:HFO2=1:7 is 0.737%and 0.460%,respectively,the corrosion resistance of Eu2O3-HfO2 is better than that of Eu2O3-ZrO2. |
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